1. Field of the Invention
The present invention relates to a converter for a polar-axis type astronomical telescope.
2. Description of the Related Art
In an equatorial telescope, the polar axis must be set parallel with the earth's axis. There is known an equatorial telescope having a polar-axis telescope in which the optical axis is identical to the polar axis to facilitate the setting operation of the polar axis. The setting operation of the polar axis of the equatorial telescope is carried out as follows. For instance, in the northern hemisphere, the Northern Star is viewed through the polar-axis telescope and the azimuth and the altitude of the equatorial telescope are adjusted so that the Polestar is located at a predetermined distance from the center of the field of view (optical axis) of the polar-axis telescope.
The number of astronomical observers is increasing who attach an electronic image pickup device (e.g., charge coupled device (CCD)) to the astronomic telescope to record an image on a video tape, such that the image can be retained for long periods of time. In particular, a need has surfaced for more precise setting of the polar axis in view of an increased precision of the electronic image pickup device (resolution or resolving power).
However, if the magnification of the polar-axis telescope is increased, the field of view of the polar-axis telescope is reduced, so that it is difficult to capture the Polestar using the polar-axis telescope. If the magnification of the polar-axis telescope is reduced, the field of view is widened, so that an observer can easily capture the Polestar, but the precision of the setting operation of the polar axis is reduced.